The bit I was missing from my implementation of `hook_farm_ui_entity_views` was the right value of `arg` which needs to be `2` to work the same as the plantings view;

```php
/**
 * Implements hook_farm_ui_entity_views().
 */
function farm_seeds_farm_ui_entity_views($entity_type, $bundle, $entity) {
  $views = array();

  // Add seed asset View at the bottom of crop/variety pages.
  if ($entity_type == 'taxonomy_term' && $entity->vocabulary_machine_name == 'farm_crops') {
    $views[] = array(
      'name' => 'farm_seeds',
      'display' => 'page',
      'arg' => 2,
      'group' => 'assets',
      'weight' => 115,
      'always' => TRUE,
    );
  }

  return $views;
}
```